sub plugin_name {
   my $text_to_return = ...;
   $text_to_return =~ s{<}{<post_include>path/to/lt</post_include>}g;
   return $text_to_return;
}

##</code><code>##

my %subst = (
   '<'     => '&lab;',
   '&lab;' => '<post_include>path/to/lab</post_include>',
);
my ($subst_re) = map qr/$_/, join '|', map quotemeta, keys %subst;

sub plugin_name {
   my $text_to_return = ...;
   $text_to_return =~ s/($subst_re)/$subst{$1}/g;
   return $text_to_return;
}